It has been known that an activated vitamin D.sub.3 has many pharmaceutical activities such as differentiation-inducing and immunoregulating actions in addition to calcium metabolic regulatory action. Up to the present time, vitamin D.sub.3 derivatives having a substituent at the 2-position have been disclosed in, for example, JP 6-23185 B and JP 6-41059 A. Among these compounds are those which are useful as a treating agent for osteoporosis.